The present invention relates generally to brake calipers, and more particularly to an electric brake caliper that allows manually-actuated parking brake application.
Conventional electric brake calipers utilize an electric motor which drives a gear assembly positioned within the caliper housing to force an inner brake pad, carried on a piston, against a brake rotor of a vehicle. An outer brake pad, mounted to a caliper housing, is positioned on an opposite side of the brake rotor. Therefore, during braking, the inner brake pad will be forced against the rotor and a resulting reactionary force will pull the outer brake pad into engagement with the opposite side of the rotor. Engagement of the inner and outer brake pads with the rotor will slow and stop the vehicle or hold a stopped vehicle in a fixed position.
A load sensor positioned to detect the amount of force applied by the inner brake pad to the rotor is operatively coupled to a mechanism for controlling the position of the caliper housing and, in turn, the force applied by the outer brake pad. Accordingly, this mechanism is used to equalize (or centralize) the force applied by the two brake pads on the rotor. An example of such a conventional electric caliber mechanism can be found in U.S. Pat. No. 4,804,073.
One disadvantage with such conventional electric brake calipers is that the electric motor operating the electric brake caliper must be actuated for the parking brake to be applied. Accordingly, if the vehicle encounters a complete loss of power, even the parking brake would not be able to be applied.
In a first expression of an embodiment of the invention, a brake caliper includes a motor, a ball screw rotatably driven by the motor, and a ball nut threadably engaged on the ball screw. The brake caliper also includes a first drive pin translatable by the ball nut, a first brake lever, and an eccentric cam shaft having a cam portion and connected to the first brake lever wherein the first brake lever and the eccentric cam shaft are rotatable by translation of the first drive pin. The brake caliper further includes a piston shaft assembly translatable by the cam portion and a piston head attached to the piston shaft assembly. The brake caliper additionally includes a brake-caliper housing having a rotor channel for receiving a rotor therein. The rotor has a first surface for engagement with a first brake pad, and the first brake pad is translatable by the piston head. In operation, the motor rotates the ball screw which translates the ball nut and the first drive pin which rotates the first brake lever, the eccentric cam shaft, and the cam portion which translates the piston shaft assembly, the piston head, and the first brake pad. In one design, the first brake lever is attachable to, and rotatable by, a manually-actuated parking brake cable. This allows operation of the parking brake to stop the vehicle in an emergency should the motor fail to operate from whatever cause including loss of power.
In a second expression of an embodiment of the invention, a brake caliper includes an electric motor, a ball screw rotatably driven by the electric motor, a ball nut threadably engaged on the ball screw, and a ball-nut housing attached to the ball nut. The brake caliper also includes a first drive pin, a first brake lever, and an eccentric cam shaft. The first drive pin is attached to the ball-nut housing and extends generally perpendicular to the ball screw. The first brake lever has an axis of rotation generally parallel to the first drive pin and includes a first groove wherein the first drive pin extends into the first groove. The eccentric cam shaft has a cam portion, is connected to the first brake lever, and has an axis of rotation generally coincident with the axis of rotation of the first brake lever. The brake caliper further includes a piston shaft assembly and a piston head attached to the piston shaft assembly. The piston shaft assembly includes an end slot and has a longitudinal axis generally perpendicular to the axis of rotation of the eccentric cam shaft wherein the cam portion is seated in the end slot. The brake caliper additionally includes a brake-caliper housing having a rotor channel for receiving a rotor therein. The rotor has a first surface for engagement with a first brake pad, and the first brake pad is attachable to the piston head. In operation, the electric motor rotates the ball screw which translates the ball nut, the ball-nut housing, and the first drive pin which rotates the first brake lever, the eccentric cam shaft, and the cam portion which translates the piston shaft assembly, the piston head, and the first brake pad. In one design, the first brake lever is attachable to, and rotatable by, a manually-actuated parking brake cable. This allows operation of the parking brake to stop the vehicle in an emergency should the electric motor fail to operate from whatever cause including loss of electric power.
In a third expression of an embodiment of the invention, a brake caliper includes a brake-caliper housing, a piston shaft assembly, a first brake pad, and an eccentric cam shaft. The brake-caliper housing includes a rotor channel for receiving a rotor therein. The piston shaft assembly is mounted in the brake-caliper housing for reciprocation into and out of the rotor channel. The first brake pad is attached to the piston shaft assembly. The eccentric cam shaft is positioned in the brake-caliper housing and has a cam portion operatively coupled to the piston shaft assembly, wherein rotation of the eccentric cam shaft in a first direction causes the piston shaft assembly to move towards the rotor channel, and wherein rotation of the eccentric cam shaft in a second direction causes the piston shaft assembly to move away from the rotor channel.
A first method of the invention is for actuating a piston shaft assembly in a brake caliper, wherein the brake caliper has a brake-caliper housing including a rotor channel for receiving a rotor therein, and wherein the piston shaft assembly is mounted in the brake-caliper housing for reciprocation into and out of the rotor channel. The method includes several steps. One step is obtaining an eccentric cam shaft having a cam portion. Then, the eccentric cam shaft is positioned in the brake-caliper housing. Next, the cam portion is operatively coupled to the piston shaft assembly so that rotation of the eccentric cam shaft in a first direction causes the piston shaft assembly to move towards the rotor channel and rotation of the eccentric cam shaft in a second direction causes the piston shaft assembly to move away from the rotor channel.
A second method of the invention is for adjusting the length of a piston shaft assembly in a brake caliper, wherein the brake caliper has a brake-caliper housing including a rotor channel for receiving a rotor therein, and wherein the piston shaft assembly is mounted in the brake-caliper housing for reciprocation into and out of the rotor channel. The method includes several steps. One step is obtaining an eccentric cam shaft having a cam portion. Then, the eccentric cam shaft is positioned in the brake-caliper housing. Another step is providing the piston shaft assembly with an adjustment screw for extending the length of the piston shaft assembly. Then, a one-way clutch assembly is operatively coupled to the adjustment screw, wherein the one-way clutch assembly is rotatable by an adjustment lever connected to the eccentric cam shaft. Finally, the adjustment lever is rotated.